1. Field of the Invention
The present invention relates to the field of semiconductor chip packaging technologies and, more particularly, to transferring solder forms to chips, chip packages or printed circuit boards.
2. Description of the Related Art
A ball grid array (BGA) chip package 10 shown in FIG. 1A solves the pin-out problem of a conventional surface mount chip package by having an array of output pads 9 on one side of the package instead of having only metal leads at the outer perimeter of the chip package. BGA Chip package 10 may have fully populated solder forms, as shown in FIG. 1B, or partially populated solder forms, as shown in FIG. 1C. Solder forms 11 are attached to chip package 10 at the end of the chip manufacturing process, and the solder form attachment occurs before chip package 10 is attached to a printed circuit board (PCB). Solder forms 11 are used to make electrical connections between chip package 10 and the PCB.
One conventional scheme for attaching solder forms 11 to chip package 10 is to position and transfer the solder forms to chip package 10 one at a time mechanically in an assembly line. Another prior art scheme is to (a) place, in the assembly line, a matrix of solder forms 21 on a fixture 23 that holds solder forms 21 temporarily and (b) transfer all of solder forms 21 to chip package 20 at once in the assembly line, as shown in FIG. 2. The advantage of the second scheme over the first is its speed. However, both schemes require sophisticated and expensive assembly equipment having stringent process controls that may cost as high as one to one and a half million dollars. Thus, it is costly and impractical to have a large number of these machines in the assembly line.
To overcome the drawbacks of the prior art, the present invention provides cost-effective and time-saving methods for transferring solder forms to IC chips, chip packages or PCBs by requiring a small number of sophisticated equipment off-line and a simplistic, reduced accuracy equipment base in the assembly line.
The present invention provides a two-step process to transfer the solder forms: (a) the solder forms are accurately positioned and placed on a roll of tape off-line using high speed, precision equipment, and (b) the solder forms on the roll of tape are transferred to the IC chips, chip packages or PCBs in the assembly line using simple, inexpensive equipment that requires less precision.
The advantages of the present invention include the following: Because the solder forms are pre-positioned on the roll of tape off-line, the process of transferring the balls to the chips, chip packages or PCBs in the assembly line can be performed much faster. The step of positioning and placing the solder forms on the roll of tape off-line saves time by performing it concurrently or independently of processing of the semiconductor chips. In addition, the present invention provides the flexibility of changing the design of the tape or the placement of the solder forms off-line and inspecting the solder forms off-line, thus not tying up the assembly line. Also, since all the modifications are made off-line, the changes can be made in a shorter amount of time. Modifying an assembly line is significantly harder than modifying off-line equipment or products since an assembly line may be used for various other products, and modifying the assembly line for one particular product line may affect other product lines. Furthermore, in the present invention, because the solder forms are pre-positioned and placed on a roll of tape, any rework or replacement of the solder forms becomes simple since the work can be performed on a low precision rework station.